The program of research focusing on adults with Down syndrome (DS), ongoing since 1987, will be continued, now consisting of four projects supported by three cores. While all of the projects have clear origins in the program's current activities, several new initiatives are included. The investigators will: (a) determine if individual differences in risk for Alzheimer's disease (AD) within the elderly population with DS is associated with insulin resistance and other features of metabolic syndrome; (b) develop empirically validated methods for identifying the presence of mild cognitive impairment (MCI) in adults with DS, differentiating this condition from cognitive changes associated with developmentally appropriate aging, per se; (c) determine the role of altered patterns of DNA methylation in DS pathogenesis and variation in phenotypic expression within this population, including selected aging-related processes; and (d) use independent datasets to evaluate the relations between age at onset of AD (as well as related phenotypic characteristics) and single nucleotide polymorphisms (SNPs) of approximately 60 candidate genes located on chromosome 21 as well as other chromosomes. As in the past, goals will be achieved through extensive collaborations among investigators representing multiple disciplines. Common assessment procedures, repeated at intervals of approximately 18 months, will be employed to characterize in detail the health, cognitive, and functional status of each of the 300 adults with DS actively participating in the program. Findings and biological samples from previous studies will also be available for the genetic and epigenetic studies now being proposed, bringing the total projected sample size to 788 adults with DS. Cognitive and functional changes will be related to selected biomarkers as well as genetic and epigenetic findings, providing a far richer description of this population than could occur in the context of any single research project. Findings should provide clear insights into: (a) mechanisms underlying important features of the DS phenotype, (b) individual differences in those features, (c) factors modifying risk for dementia, and (d) assessment methods that can inform diagnostic decisions relatively early in disease progression. Further, some findings may have direct implications for promoting more successful aging for adults with DS.